drm/i915: Kill private_default_ctx off

It's barely alive now anyway, so give it the "coup de grâce".

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/i915_debugfs.c
Simple merge

diff --cc drivers/gpu/drm/i915/i915_drv.h
Simple merge

diff --cc drivers/gpu/drm/i915/i915_gem_context.c
Simple merge